This invention relates to a method for enhancing the corrosion resistance of aluminum and aluminum alloys by deposition of a cerium-based coating thereon. The invention has particular application for aerospace structural components such as aircraft skin, wing skin and other sheet components manufactured from aluminum or aluminum alloys, especially sheet and bulk structural pieces, or in other applications where long-term corrosion resistance is desired.
Many aerospace components are constructed from aluminum or aluminum alloys due to their superior strength to weight ratio.
Aluminum and aluminum alloys, however, are subject to corrosion upon exposure to water condensed from humid air and contaminated from other sources with salt, rain, snow, ocean salt, salt applied to runways, and other environmental conditions, which can lead to catastrophic failure. Heretofore the corrosion resistance of aluminum and aluminum alloys has been enhanced by the use of chromate conversion coatings. A conversion coating is a coating consisting of metallic salts, such as chromate, which form during and after dissolution of a metallic element, such as chromium or aluminum, or are precipitated from salts onto a substrate. A disadvantage of chromate coatings, however, is their toxicity, as ingestion or inhalation of chromates has been determined to cause kidney failure, liver damage, blood disorders, lung cancer and eventually death. Corrosion resistance has also been enhanced by anodizing. However, anodizing is known to cause fatigue problems leading to failure of aluminum components.
Stoffer et al. U.S. Pat. No. 5,932,083 discloses electrodeposition of cerium-based components onto aluminum substrates.
Among the several objects of this invention, therefore, is the enhancement of the corrosion resistance of aluminum and aluminum alloy aircraft components; the enhancement of corrosion resistance of such components without reducing fatigue resistance; the enhancement of the corrosion resistance of aluminum and aluminum alloys using materials which are not toxic in the relevant concentrations; the enhancement of the corrosion resistance of aluminum and aluminum alloys using a cerium-based coating produced by electrodeposition resulting in spent electrolyte having minimal negative environmental impact.
Briefly, therefore, the invention is directed to a process for enhancing the corrosion resistance of an aluminum-containing component in which an aluminum-containing cathode and an oxygen-evolving anode are immersed in an electrolyte comprising water, cerium ions, and animal gelatin or derivative or components thereof, and an electrical current is passed through the electrolyte to deposit a cerium-based coating onto the aluminum-containing cathode.
Other objects and features of the invention will be in part apparent, and in part described hereafter.